1. Field of the Invention
The present invention relates to an ultrasound imaging apparatus that transmits ultrasound waves to the subject, generates an ultrasound image based on reflected waves from the subject and displays the ultrasound image, and also relates to a method for displaying an ultrasound image. In particular, the present invention relates to an ultrasound imaging apparatus that obtains quantitative information of tissue shown in an ultrasound image, and also relates to a method for displaying an ultrasound image.
2. Description of the Related Art
An ultrasound imaging apparatus transmits ultrasound waves to the subject and generates ultrasound image data representing the morphology of tissue within the subject based on reflected waves from the subject. An ultrasound imaging apparatus according to a conventional art has a function of measuring the size of tissue such as a lesion site and organ shown in an ultrasound image. For example, the ultrasound imaging apparatus is provided with a function of measuring the distance between two points in tissue like a lesion site, a function of measuring the perimeter of tissue, a function of measuring the area of tissue, etc.
In the abovementioned measurement functions, a measurement marker called a measurement caliper is displayed on an ultrasound image. This measurement caliper can be moved on a screen with an input device such as a trackball. An operator fits the position of the measurement caliper to the position of a site to be measured shown in an ultrasound image. The ultrasound imaging apparatus obtains a quantitative value by measuring the size of tissue designated with the measurement caliper. For example, it is possible to designate two points on an ultrasound image with the measurement caliper to measure the distance between the designated two points.
Further, a plurality of ultrasound images may be displayed side by side to measure the size of a measurement target shown in each of the ultrasound images. For example, in the case of simultaneous display of two ultrasound images, conventionally, a measurement caliper is displayed on one of the ultrasound images, and the operator moves the measurement caliper to the position of a measurement target to measure the size of the measurement target shown in the one ultrasound image. Next, the measurement caliper is displayed on the other ultrasound image, and the operator moves the measurement caliper to the position of a measurement target to measure the size of the measurement target shown in the other ultrasound image. Thus, conventionally, the measurement is executed by individually operating the measurement caliper in each of the ultrasound images and designating a measurement target shown in each of the ultrasound images.
Further, there is a known method of displaying a B-mode image captured in the B-mode and an M-mode image captured in the M-mode side by side to obtain the quantitative value of a measurement target shown in the B-mode image in a case that a measurement caliper is on the B-mode image whereas obtain the quantitative value of a measurement target shown in the M-mode in a case that the measurement caliper is on the M-mode image (Japanese Examined Patent Publication No. 62-4978).
Further, there is a method of simultaneously displaying two ultrasound images, and displaying a cursor in a designated position on one of the ultrasound images, whereas displaying another cursor on the other ultrasound image in a position corresponding to the designated position on the one ultrasound image (Japanese Unexamined Patent Publication No. 11-221216).
However, in the case of simultaneously displaying a plurality of ultrasound images, it is difficult for the operator to grasp the positional relation between the images. Therefore, it is difficult for the operator to observe a plurality of ultrasound images, move a measurement caliper to positions corresponding to each other on the plurality of ultrasound images, and measure the size of measurement targets.
Further, by injecting a contrast agent into the subject and imaging, it is possible to generate a contrast enhanced image in which a site with the contrast agent injected is enhanced. For example, by injecting a contrast agent into the subject and imaging by Contrast Harmonic Imaging (CHI), it is possible to generate a harmonic image based on harmonic waves. Then, a body tissue image representing the morphology of body tissue and a contrast enhanced image obtained in contrast imaging are simultaneously displayed. A body tissue image shows, for example, the morphology of tumor. Moreover, a contrast enhanced image shows a site with microbubbles of a contrast agent injected is enhanced. Even in the case of thus simultaneously displaying a body tissue image and a contrast enhanced image, it is difficult for the operator to grasp the positional relation between the tumor shown in the body tissue image and the site with the contrast agent injected shown in the contrast enhanced image. Therefore, it is difficult for the operator to determine whether or not the contrast agent is injected in the tumor based on the body tissue image and the contrast enhanced image. Besides, a method of displaying the contrast enhanced image and the body tissue image in the superimposed state is known, but there is a problem that contrast resolution (gradation) decreases because the two images are superimposed on each other.
Additionally, when the contrast enhanced image is superimposed on the body tissue image, the body tissue image is hidden behind the contrast enhanced image. Therefore, it is difficult for the operator to grasp the accurate positional relation between the site with the contrast enhanced image injected and the tissue shown in the body tissue image.
As described above, it is difficult for the operator to grasp the image positional relation between the body tissue image and the contrast enhanced image. Therefore, it is difficult to move the measurement caliper to the corresponding positions on the body tissue image and the contrast enhanced image to designate the measurement targets.
Further, the abovementioned method described in Japanese Examined Patent Publication No. 62-4978 is a method of executing the measurement on the image with the measurement caliper displayed of the B-mode image and the M-mode image. Therefore, it is difficult for the operator to execute the measurement by moving the measurement caliper to the corresponding positions on the plurality of ultrasound images. Besides, in the method described in Japanese Unexamined Patent Publication No. 11-221216, the measurement using the measurement caliper is not executed. Therefore, it is difficult to execute the measurement in the corresponding positions on the plurality of ultrasound images.